[misc] bump metrics module to 3.4.1

- renamed package from `metrics-sharelatex` to `@overleaf/metrics`
- drop support for statsd backend
- decaffeinate
- compress `/metrics` response using gzip
- bump debugging agents to latest versions
- expose prometheus interfaces for custom metrics (custom tags)
- cleanup of open sockets metrics
- fix deprecation warnings for header access

services/notifications/test/unit/js/NotificationsControllerTest.js

@@ -29,7 +29,7 @@ describe('Notifications Controller', function () {
       requires: {
         'logger-sharelatex': { log() {} },
         './Notifications': this.notifications,
-        'metrics-sharelatex': {
+        '@overleaf/metrics': {
           inc: sinon.stub()
         }
       }